When a sample is irradiated while scanning with electrons and secondary charged particles released from the sample are detected, the structure of the surface of the sample can be observed. This is called a scanning electron microscope (hereinbelow, abbreviated as SEM). On the other hand, also by irradiating a sample while scanning with an ion beam and detecting secondary charged particles released from the sample, the structure of the sample surface can be observed. This is called a scanning ion microscope (hereinbelow, abbreviated as SIM). Particularly, when a sample is irradiated with an ion species which is light in mass such as hydrogen or helium, sputtering action becomes relatively small, and it becomes suitable to observe a sample.
Further, the ion beam is more sensitive to information of a sample surface as compared with an electron beam. The reason is that an excitation region of secondary charged particles locally exists more in the sample surface as compared with irradiation of the electron beam. In the electron beam, since the nature as waves of electrons cannot be ignored, an aberration is caused by the diffractive effect. On the other hand, since the ion beam is heavier than electrons, the diffractive effect can be ignored.
By irradiating a sample with an ion beam and detecting ions passed through the sample, information in which the structure of the inside of the sample can also be obtained. This is called a transmission ion microscope. In particular, by irradiating a sample with an ion species which is light in mass such as hydrogen or helium, the ratio of passing through the sample increases, and it is preferable for observation.
On the other hand, by irradiating a sample with an ion species which is heavy in mass such as argon, xenon, or gallium, it is preferable to process the sample by sputtering action. In particular, a focused ion beam (hereinbelow, abbreviated as FIB) device using a liquid metal ion source (hereinbelow, abbreviated as LMIS) is known as an ion beam processor. In recent years, a composite FIB-SEM device of a scanning electron microscope (SEM) and a focused ion beam (FIB) is also used. In the FIB-SEM device, by forming a square hole in a desired place with irradiation of an FIB, a section can be SEM-observed. A sample can also be processed by generating a gas ion of argon, xenon, or the like by a plasma ion source or a gas field ion source and irradiating a sample with the gas ion.
In the ion microscope, a gas field ion source is preferable as the ion source. The gas field ion source supplies gas of hydrogen, helium, or the like to a metal emitter tip having a tip curvature radius of about 100 nm, applies a high voltage of a few kV or higher to the emitter tip to ionize gas molecules, and extracts the resultant as an ion beam. As characteristics, the ion source can generate an ion beam having a narrow energy width and, since the size of the ion generation source is small, generate a fine ion beam.
In the ion microscope, to observe a sample at a high signal-noise ratio, an ion beam of high current density has to be obtained on a sample. For this purpose, the ion radiation angle current density of the ionization ion source has to be made high. To make the ion radiation angle current density high, it is sufficient to increase molecule density of ion material gas (ionization gas) in vicinity of the emitter tip. The gas molecular density per unit pressure is inversely proportional to temperature of gas. Consequently, it is sufficient to cool the emitter tip to extremely low temperature and decrease the temperature of gas around the emitter tip to low temperature. By the operation, the molecule density of the ionization gas in the vicinity of the emitter tip can be made high. The pressure of the ionization gas around the emitter tip can be set to, for example, about 10−2 to 10 Pa.
However, when the pressure of the ion material gas is set to 1 Pa or higher, the ion beam collides with neutral gas, and the ion current decreases. When the number of gas molecules in the field ion source becomes large, the frequency that gas molecules which collide with the wall of a high-temperature vacuum vessel and come to have high temperature collide with the emitter tip increases. Due to this, the temperature of the emitter tip rises, and the ion current decreases. Consequently, the field ion source is provided with an ionization chamber mechanically surrounding the emitter tip. The ionization chamber is formed by using an ion extraction electrode provided so as to be opposed to the emitter tip.
Patent Reference 1 discloses a method of improving the ion source characteristic by forming a small projection at the end of the emitter tip. Non-patent Reference 1 discloses a method of manufacturing the small projection at the end of the emitter tip by using a second metal different from the material of the emitter tip. Non-patent Reference 2 discloses a scanning ion microscope having a gas field ion source for ion-emitting helium.
Patent Reference 2 discloses a method of providing, in positions apart from each other in the circumferential direction of a side wall of a vacuum vessel of an ion source, a plurality of supporting pieces for vibration prevention extending from the inner face of the side wall toward the ion source and whose length can be adjusted from the outside so as to penetrate, and sandwiching a heat insulating material between the inner end of each of the supporting piece and the supporting face to press the ion source, thereby preventing vibration of the ion source. However, inflow of heat from the supporting pieces to the ion source is not considered.
Patent Reference 3 discloses a method of making a spherical device float in a predetermined position over a superconductor material at the time of exposing the sphere device to light.
Patent Reference 4 discloses a liquid metal ion source having a needle-shaped member as an ion emitter, an extraction electrode, and an acceleration electrode, wherein an opening through which an extracted ion passes is provided on the side opposed to the needle-shaped member of the acceleration electrode, and a shield member for preventing sputter particles generated by collision of the extracted ions with each other or with the acceleration electrode from reaching the needle-shaped member is provided.
Patent Reference 5 discloses an electron beam device having a movable diaphragm which can be inserted from a passage of an electron beam, wherein a spare chamber which is communicated with the electron beam device body in vacuum and can be shielded by air lock means, and means for evacuating the spare chamber are provided, and the movable diaphragm is moved to the spare chamber without exposing the electron beam device body to atmosphere, and can be replaced. In the device, without exposing the electron beam device body to atmosphere, the movable diaphragm which is contaminated can be easily replaced or cleaned.
Patent Reference 6 discloses a charged particle beam device which is downsized by using a non-evaporable Getter pump, not an ion pump, as main exhaust means of the electron source.
Patent Reference 7 discloses a gas field ion source provided with a change-over switch for connecting a high-voltage lead-in wire for the extraction electrode to a high-voltage lead-in wire for the emitter tip. In the gas field ion source, after forced discharge process between the ion source outer wall and the emitter tip, that is, so-called conditioning process, discharge between the emitter tip and the extraction electrode can be prevented.
Patent Reference 8 proposes an apparatus for observing and analyzing a failure, a foreign matter, or the like by forming a square hole near an abnormal place in a sample with an FIB and observing the section of the square hole by an SEM device.
Patent Reference 7 proposes a technique of extracting a small sample for transmission electron microscope observation from a bulk sample by using an FIB and a probe.